The invention relates to a reflector for an oblong light source, comprising a conical part to which a curved part connects, said parts being provided on the inside with longitudinal grooves.
Light fittings with downward-directed light beams are used, for example, to direct light from the ceiling onto, say, the floor. Here, reflectors are used to direct the light as well as possible onto the object. For point-shaped light sources, virtually ideal reflector forms can be calculated, because point-shaped light sources do not stand in the way of the light beams reflected by the reflector. In particular, light distributions in which the light intensity increases as the angle relative to the centre line of the reflector increases can be achieved. By means of such light intensity distributions, which are also described as wing-shaped, a light intensity distribution which is as uniform as possible can be obtained on the area to be illuminated, for example the floor.
Oblong lamps, such as compact fluorescent lamps are not point-shaped and therefore have a light-radiating and, conversely also, a light-absorbing surface which is so large compared with the dimensions of the reflector that the lamp constitutes a hindrance for the light rays coming from the reflector. This means that, without additional measures, only light intensity distributions which are at a maximum at or near the reflector centre line can be obtained.
In order to obtain a wing-shaped light distribution, applicants have developed a reflector cap, comprising a conical and a curved part. These parts are provided with longitudinal grooves. Viewed in the cross section of the reflector, the said longitudinal grooves are preferably triangular in shape. In this way, the light rays falling on the walls of the grooves are deflected in such a way that they run along the oblong light source and thus contribute to a wing shaping of the light intensity distribution.
A precise calculation of the light intensity distribution which can be expected is almost impossible due to the multiple reflections, and it would be too inaccurate, while the physical conditions have to be idealised. That is why, for the determination of the light intensity distribution produced by the longitudinal grooves or facets, one is dependent on measurements. Depending on the design of the reflector, it always happens that a further correction of the reflector is hardly possible, for example if material had to be added in the equipment for making the reflector in order to achieve the desired shape. Corrections of the curves of the curved part are very difficult to carry out and give rise to high costs. Despite the great difficulty and the costs, a uniform lighting intensity is not achieved. Moreover, the grooves give rise to a rotationally symmetrical wing-shaped light intensity distribution which means that, in a plane perpendicular to the centre line of the lamp, a light distribution is produced in which the light intensity is less in the centre than outside the centre.